A (+ -)-CYCLOCYTIDINE ANALOG WITH A LOW-ANTI CONFORMATION AROUND THE GLYCOSYL BOND/

The crystal structure of the cytidine analogue '-anhydro-2'-deoxy-6,6' beta-dihydroxycarbacytidine hydrate (alternative name: 3 droxymethyl-6 ,7,8,8a-tetrahydro-1H,5aH-cyclopenta[ 1',2':1,2]oxazolo[3,2-c]pyrimidi n-1-one hydrate), C10H13N3O4.H2O, in which the, glycosyl torsion angle was fixed by cyclization between the C6' atom of the cyclopentane rin g and the C6 atom of the cytosine base with one O atom, was determined by X-ray analysis. The crystal belongs to the monoclinic space group P2(1)/c and the unit cell contains four cytidine analogue and four wat er molecules. The terminal O5' atom of the cytidine analogue molecule is hydrogen bonded to a water molecule. The glycosyl torsion angle is low-anti (chi = 176.3 degrees) and the puckering of the cyclopentane r ing is C3'-envelope.